Component mounting board inspecting apparatus

ABSTRACT

There is provided a component mounting inspecting apparatus which can automatically set a solder bridge inspection region (an inspection point), and output an optimum inspection result of a solder bridge. The component mounting board inspecting apparatus for inspecting a solder bridge of an electronic circuit board, in which a plurality of electrode pads are formed at predetermined spaced intervals, and cream solder is applied on the electrode pads, includes mechanism for automatically determining a distance between adjacent electrode pads; and mechanism for automatically setting a solder bridge inspection point if the distance between the adjacent electrode pads is equal or shorter than a threshold value.

CROSS REFERENCE TO RELATED APPLICATONS

The present document is based on Japanese Priority DocumentJP2004-032567, filed to the Japanese Patent Office on Feb. 9, 2004, thecontents of which being incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a component mounting board inspectingapparatus for inspecting for defects in cream solder printed on anelectrode pad of a component mounting board, and more specificallyinspecting whether there are solder bridges generated between adjacentelectrode pads.

2. Description of Related Art

On a component mounting board such as a printed board for mounting anumber of components of a semiconductor device and the like, a number ofelectrode pads are formed corresponding to the number of electrodes ofthese components, and a wiring circuit pattern. In order to solder thesecomponents, cream solder is printed on the electrode pads by screenprinting method, for example. If the cream solder is not suitablyprinted on the electrode pads, the components cannot be desirablysoldered. Therefore, before soldering the components on the componentmounting board, it is inspected whether or not the cream solder issuitably printed on each electrode pad by the use of a componentmounting board inspecting apparatus.

A functional block diagram of such component mounting board inspectingapparatus is shown in FIG. 4, in which reference numeral 100 indicates acomponent mounting board inspecting apparatus. The component mountingboard inspecting apparatus 100 has an annular illuminating apparatus110, a camera 120 such as a CCD cameral, an image processor 130, acontrol unit 140, and a result indicator 150.

The illuminating apparatus 110 facilitates observation of a componentmounting board B. The camera 120 captures a visual image of thecomponent mounting board B illuminated by the illuminating apparatus110. The image processor 130 captures the image outputted from thecamera 120, and then executes an inspection algorithm. The control unit140 controls the brightness of the illuminating apparatus 110, and thedrives of the illuminating apparatus 110 and the camera 120. The resultindicator 150 indicates an obtained inspection result.

A method of determining as to whether cream solder is suitably printedor not is made as follows: the printed state of the cream solder on thecomponent mounting board B is compared with the information captured bythe image processor 130, based on the information of printing of creamsolder (the printing area of the cream solder, the printing width of thecream solder, and the printing position of the cream solder), which arepreset in the component mounting board inspecting apparatus 100.

In the cream solder inspection method, the object to be inspected issolder subjected to reflow, instead of cream solder. This kind ofinspection is disclosed in Japanese Patent Application Laid-Open No.10-160426 (page 1, and abstract), for example.

A variety of electrode pads are formed on the component mounting boardB, such that a variety of components, including various semiconductordevices, are mountable thereon. A plurality of electrode pads 1A, 1B,1C, . . . , are formed in a predetermined array on the componentmounting board B, and the pad-to-pad distance of these electrode padswill vary over different portions, as partially shown in FIG. 5(electrode pads having a large pad-to-pad distance are not shown).Referring to FIG. 5, the pad-to-pad distance of the electrodes pads 1A,1B, 1C, . . . , which mount, for example, a ball grid array (BGA) typeIC and a quad flat package (QFP) type IC, is considerably narrow (or,short), for example, about 500 μm or less. When cream solder S isprinted on the electrode pads 1A, 1B, 1C, . . . , by screen printingmethod, etc., as shown in FIG. 6, it is desirable that the cream solderS is printed so as not to spread beyond the electrode pad 1B. However,as shown in FIG. 7, the cream solder S on a certain electrode pad, forexample, the electrode pad 1A, may bridge the electrode pad 1B adjacentto the right side. This is a so-called solder bridge Sb. Needless tosay, the occurrence of the solder bridge Sb is undesirable, and hencethis must be reliably detected, and the component mounting board Binvolving the solder bridge Sb must be removed from the line.

Conventionally, in creating an inspection program for detecting thesolder bridge Sb, between the pads at which a solder bridge Sb is likelyto occur, an operator manually sets a bridge inspection point Pbindicated by the dotted lines, which is extended to electrode padsadjacent to an inspection point Pa for observing the electrode pads 1A,1B, 1C, . . . . There is no need for setting the bridge inspection pointPb between electrode pads having a large pad-to-pad distance D, and itis only necessary to set the inspection point Pa at which the state ofthe cream solder S on each electrode pad is observed.

Consequently, if an operator performs inspection without making anymanual setting, despite a defect due to a solder bridge, this may bedetected as another kind of defect, or be even overlooked.

In addition, there are the following limitations in that: with respectto a solder bridge inspection region, it is required to indicate theinspection point Pb individually as above described; and that theinspection point Pb can be pasted (copied) only to the same pattern onthe component mounting board B. Thus, considerable amount of time isrequired for creating data designating a solder bridge inspection region(an inspection point) Pb.

SUMMARY OF THE INVENTION

The present invention has been conceived in view of the above mentionedproblems and a preferred embodiment of the present invention provides acomponent mounting board inspecting apparatus, which can automaticallyset a solder bridge inspection region (an inspection point), and outputan optimum inspection result of a solder bridge.

According to a preferred embodiment of the present invention, acomponent mounting board inspecting apparatus for inspecting a solderbridge of an electronic circuit board, in which a plurality of electrodepads are formed at predetermined spaced intervals and cream solder isapplied on the electrode pads, includes mechanism for automaticallydetermining a distance between adjacent electrode pads; and mechanismfor automatically setting a solder bridge inspection point if thedistance between adjacent electrode pads is equal or shorter than a setpredetermined threshold value.

According to another preferred embodiment of the present invention, acomponent mounting board inspecting apparatus includes: illuminatingunit adapted to illuminate a component mounting board on which aplurality of electrode pads are formed at spaced intervals; a imagingdevice adapted to image-capture the illuminated component mountingboard, and outputting image data; a binarizer adapted to binarize theimage data; a binarized image storage unit adapted to store thebinarized image; a position coordinate acquiring unit adapted to acquirea position coordinate of each of the electrode pads from the storedbinarized image; a near distance measuring unit adapted to measure apad-to-pad distance of an electrode pad adjacent to the positioncoordinate of each of the electrode pads; a comparator adapted tocompare the pad-to-pad distance with a threshold value; and a solderbridge inspection point setting unit adapted to set a solder bridgeinspection point if the pad-to-pad distance is shorter than thethreshold value.

Therefore, in accordance with the component mounting board inspectingapparatus of a preferred embodiment of the present invention, a solderbridge inspection point (region) can be set automatically. Because ofthis, an operator is able to output an optimum inspection result withoutspending the labor and the time involved in manual setting.

Additionally, in a variety of component mounting boards in which it isexpected that there will be further complication, optimum setting of asolder bridge inspection point (region) is attainable only by setting athreshold value.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following description ofthe presently preferred exemplary embodiments of the invention taken inconjunction with the accompanying drawings, in which:

FIG. 1 is a schematic functional block diagram of a component mountingboard inspecting apparatus of a preferred embodiment of the presentinvention;

FIG. 2 is a flowchart showing a procedure to set a solder bridgeinspection point in a preferred embodiment of the present invention;

FIG. 3 is a plan view partially showing an electrode pad array having ashort pad-to-pad distance, for the purpose of explaining the setting ofa solder bridge inspection point;

FIG. 4 is a functional block diagram of a component mounting boardinspecting apparatus;

FIG. 5 is a plan view partially showing a component mounting board (abare board), on which electrode pads are formed at short pad-to-paddistances;

FIG. 6 is a plan view partially showing a component mounting board, inwhich cream solder is suitably printed; and

FIG. 7 is a plan view partially showing a component mounting board, inwhich cream solder is printed, causing occurrence of a solder bridge.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Example of Preferred Embodimentof the Present Invention

A component mounting board inspecting apparatus of a preferredembodiment of the present invention will next be described by referenceto the drawings.

FIG. 1 is a schematic functional block diagram of a component mountingboard inspecting apparatus of a preferred embodiment of the presentinvention. FIG. 2 shows a flowchart showing a procedure to set a solderbridge inspection point in a preferred embodiment of the presentinvention. FIG. 3 is a plan view partially showing an electrode padarray having a short pad-to-pad distance, for the purpose of explainingthe setting of a solder bridge inspection point.

Referring now to FIG. 1, a description will be made of a componentmounting board inspecting apparatus 11 of a preferred embodiment of thepresent invention.

In FIG. 1, reference numeral 1 indicates this component mounting boardinspecting apparatus. The component mounting board inspecting apparatus11 can broadly be classified into an image capturing unit (A) and animage processor (B).

A component mounting board (a so-called bare board) Bb, on which creamsolder S to be inspected is not printed, is situated on a table 12.

The image capturing unit (A) is composed of a first illuminating unit13A for irradiating a predetermined irradiation light to the componentmounting board Bb, along the normal to the bottom surface of thecomponent mounting board Bb; a second illuminating unit 13B forirradiating predetermined irradiation light to the component mountingboard Bb, in the direction in which a predetermined angle is formed withthe normal, and irradiating from the surroundings of the componentmounting board Bb; a third illuminating unit 13C for irradiating thecomponent mounting board Bb with irradiation light making a furthergreater angle than the predetermined angle to the normal of the secondilluminating unit 13B; and a camera 15 disposed in the normal to thebottom surface of the component mounting board Bb. The camera 15captures, as image, the reflected light from the surface of thecomponent mounting board Bb, which is derived from the irradiation lightemitted from at least one selected from the first illuminating unit 13A,the second illuminating unit 13B, and the third illuminating unit 13C.

An analog signal outputted from the camera 15 is subjected to ADconversion by an analog/digital (AD) converter 16 for converting to adigital signal, and the digital signal is inputted to the imageprocessor (B). The image processor (B) includes a binarizer 17, abinarized image storage unit 18, a position coordinate acquiring unit19, a near distance measuring unit 20, and a comparator 21 for comparinga near distance with a threshold value.

Fetched as characteristic values of the component mounting board Bb arethe area and the position (x-y coordinates) of each electrode pad on thecomponent mounting board Bb. Therefore, the respective characteristicvalues are detected in association with the area and the position of aregion on the image formed by the location where there is irradiationlight having intensity at least equal or higher than a predeterminedlevel.

The first illuminating unit 13A may be any one, which is constructedsuch that illumination is irradiated uniformly from above the normal ofthe component mounting board Bb to the component mounting board Bbaround approximately the center of the component mounting board Bb.

The second illuminating unit 13B may be any one, which is constructed toirradiate light from obliquely above the component mounting board Bb,and have its reflected light enter the camera 15.

The third illuminating unit 13C is preferably constructed to irradiateinspection light to the component mounting board Bb from the directionin which there is formed a greater angle than the angle defined betweenthe normal direction of the component mounting board Bb of the secondilluminating unit 13B and the above-mentioned obliquely above direction.Although the angle thereof is not particularly limited, it is preferablyconstructed to irradiate from obliquely above, which is as horizontal aspossible to the component mounting board Bb.

The first illuminating unit 13A, the second illuminating unit 13B andthe third illuminating unit 13C can be driven independently orsimultaneously, and depending on the type of the component mountingboard Bb to be inspected, any one of these units is usable. A controller14 is disposed to control the illuminating units 13A, 13B and 13C.

On the other hand, the camera 15 is preferably disposed substantiallyabove the component mounting board Bb, such that the central opticalaxis of the camera 15 is arranged on the normal line of substantiallythe center of the component mounting board Bb. The camera 15 is alsopreferably a camera that can capture the reflected light from thecomponent mounting board Bb, as image information. For example, a CCDcamera is usable.

In the component mounting board inspecting apparatus 11, theilluminating units and the camera 15 move integrally to underneath thecontroller 14, and a large number of points to be inspected, forexample, as many as 4000 points, are sequentially scanned under apredetermined program. Then, the analog information outputted from thecamera 15 is inputted, via the AD converter 16 for converting to digitalinformation, to the image processor (B) for executing a predeterminedimage processing. Based on the digital signal from the AD converter 16,the image processor (B) selects and extracts the reflected lightindicating a reflected light intensity exceeding a predeterminedreference value, from the reflected lights reflected from the surface ofthe component mounting board Bb, and then creates an image indicatingthe location of the component mounting board Bb, from which thereflected light indicating the reflected light intensity exceeding thepredetermined reference value is generated.

Specifically, the image processor (B) includes the binarizer 17 forexecuting binarization by applying a predetermined threshold value toinputted digital information; the binarized image storage unit 18 forcreating and storing an image based on the binarized data obtained fromthe binarizer 17; the position coordinate acquiring unit 19 foracquiring the position (x-y coordinates) data of each electrode pad fromthe binarized image data stored in the binarized image storage unit 18;the near distance measuring unit 20 for measuring a pad-to-pad distance(a near distance) of adjacent electrode pads from the position (x-ycoordinates) data of each electrode pad; and the between near distanceand threshold comparator 21 for comparing the measured pad-to-paddistance with a threshold value manually initialized by an operator,etc.

The initialized threshold value is the distance that can be judged asbeing susceptible to a solder bridge of the pad-to-pad distance D ofeach electrode pad formed on the component mounting board Bb. Forexample, based on the background information that the pad-to-paddistance D of the electrode pads 1A, 1B, 1C, . . . , which mount the BGAtype IC and the QFP type IC as shown in FIG. 5, is considerably short,and the pad-to-pad distance is as short as about 500 μm, as abovedescribed, the value of 500 μm is initialized as a threshold value.

The operation of the component mounting board inspecting apparatus 11will next be described with reference to FIG. 2 and FIG. 3.

First, the component mounting board (bare board) Bb, in which creamsolder is not printed on electrode pads, etc., is situated and securedto the table 12. Then, the irradiation light from any one of theilluminating units, for example, the second illuminating unit 13B, isirradiated sequentially from obliquely above to the respective electrodepads of the component mounting board Bb. Then, the binarizer 17binarizes their respective images, and their binarized images arewritten in the binarized image storage unit 18 (step S1).

Subsequently, the position coordinate acquiring unit 19 captures thecoordinates in the X-axis direction and the Y-axis direction of therespective electrode pads (step S2), and the near distance measuringunit 20 measures the side coordinates of the respective electrode pads,that is, the pad-to-pad distance of adjacent electrode pads.

The between near distance and threshold comparator 21 compares thepad-to-pad distance (the near distance) measured by the near distancemeasuring unit 20 with a previously initialized threshold value, forexample, 500 μm (step S4). When the pad-to-pad distance is equal orshorter than the threshold value, a solder bridge inspection point Pb,at which solder bridge inspection is executed, (the hatching area) iscreated (step S5). If the pad-to-pad distance is equal or larger thanthe threshold value, the solder bridge inspection point Pb, at whichsolder bridge inspection is executed, is not created, and only aninspection point Pa is created (step S6).

When creating the solder bridge inspection point Pb, as shown in FIG. 3,the solder bridge inspection point Pb is created only on the right sideof the respective electrode pads 1A, 1B, 1C, . . . , and on the upperside of the respective electrode pads 1D, 1E, 1F, . . . . It is set suchthat an operator will be informed of by speech generation of “solderbridge defect on the right side,” and “solder bridge defect on the upperside” at each inspection point. Herein, the pad-to-pad distance D isshorter than the threshold value.

Thus, by virtue of the automatic setting of the solder bridge inspectionpoint in the component mounting board inspecting apparatus 11, thecomponent mounting board Bb, in which cream solder is printed on eachelectrode pad, is situated on the table 12, and the image capturing unit(A) is moved sequentially as above described, then the camera 15captures image under illumination of any one of the illuminating units.When detected a portion smaller than the threshold value of thepad-to-pad distance D, the solder bridge inspection point Pb is expandedautomatically between the pads, and it is detectable whether the solderbridge Sb is generated or not, as shown in FIG. 7. If the solder bridgeSb is detected, the cream solder portion thereof may be colored red, forexample, in order to let an operator easily recognize this on the imageindicator.

Therefore, according to the example of embodiment of component mountingboard inspecting apparatus of the present invention, the inspectionpoint for the solder bridge may be automatically set and, as a result,the operator may output a desirable inspection result without spendingtime or requiring effort for manually setting the point.

Though a preferred embodiment of the present invention has beendescribed herein in its preferred form through examples of preferredembodiments thereof with a certain degree of particularity, the presentinvention should not be construed as to be limited to such examples ofpreferred embodiments presented herein, so that various modifications,variations, combinations, sub combinations as well as differentapplications thereof are possible without departing from the scope ofthis invention. For example, though reference has been made in thepreferred embodiments to a camera to work as an imaging device, manyother types of imaging apparatus or devices may be used, such as imagingelements or other elements that would function to capture light forimaging purposes or capturing signals and/or information for similarpurposes.

1. A component mounting board inspecting apparatus configured toinspecting a solder bridge of an electronic circuit board, on which aplurality of electrode pads are formed at spaced intervals and creamsolder is applied on the electrode pads, the apparatus comprising:mechanism for automatically determining a distance between adjacentelectrode pads; and mechanism for automatically setting a solder bridgeinspection point if the distance between adjacent electrode pads isequal or shorter than a threshold value.
 2. A component mounting boardinspecting apparatus comprising: an illuminating unit adapted toilluminate a component mounting board on which a plurality of electrodepads is formed at spaced intervals; a imaging device adapted toimage-capture the illuminated component mounting board, and outputtingimage data; a binarizer adapted to binarize the image data; a binarizedimage storage unit adapted to store the binarized image; a positioncoordinate acquiring unit adapted to acquire a position coordinates ofeach of the electrode pads from the stored binarized image; a neardistance measuring unit adapted to measure a pad-to-pad distance of anelectrode pad adjacent to the position coordinate of each of theelectrode pads; a comparator adapted to compare the pad-to-pad distancewith a threshold value; and a solder bridge inspection point settingunit adapted to set a solder bridge inspection point if the pad-to-paddistance is shorter than the threshold value.